Printing-telegraph-exchange system



March 1927.,

G. s. VERNAM PRINTING TELEGRAPH EXCHANGE SYSTEM 2 Sheets-Sheet 1 Filed Dec. 25, 1922 E EmEF w Lm E LwEEmcBLH 1 Huh. I

Q\ .7 QL M //7 val 270k: Gi/b er! 5. Vern am. by %r u m 97 March 1927 G. s. \IERNAM 9 PRINTiNG TELEGRAPH EXCHANGE SYSTEM Filed Dec. 23, 1922 2 Sheets-Sheet 2 Patented 8, 1927.

UNITED STATES 1,619,897 PATENT. OFFICE.

GILBERT s. VERNAM, or BROOKLYN, NEW YORK, ASSIGNOR T0 AMEnIoAN TELE- PHONE AND TELEGRAZPH company, AcoRroRA'rIoN or NEW'YORK.

PRINTING-TELEGRAPH-EXCHANGE SYSTEM.

Application filed December This invention relates to printing telegraphy, and particularly to exchange systems.

Its object isa printing telegraph exchange system vvherein repeating means is associated with the link circuits for repeating impulses between connected lines.-

The invention according-to its preferred form provides. a printing telegraph exchange system in which a plurality of printing telegraph subscribers lines terminate ata central office where l nk ClICllltS are cated for establishing connections between the subscribers lines In each of the link circuits there is arranged repeating means whereby the impulses from one linewill be transmitted accordingly to the connected line, thus permitting the use of the'equip- I'ncnt in conjunction with lines in which the associated stations are located at remotely separated points.

A better understanding of the invention may be had, from the following description,-

taken in conjunction with the accompanying drawings which illustrate the invention.

Referring to the drawings, Fig. 1 'lllllS- trates one'embodiment of the invention, while Fig. 2, represents a mod fication of' the arrangement shown in Fig. 1.

Referring now to Fig. .1, there are shown two printing telegraph subscribers stations,- A and B, having telegraph lines, D and E, respectively, connecting the stations with a central oflice C. It Wlll be understood, of

course. tha'tin actual practice many other lines similar Ito'D and E may terminate at the same central office, and that a plurality of link circuits similar to C are .employed and each-of the. link circuits is arranged with direct point repeating means for repeating directly the'impulses received from one line to another line with which it is associated through the link circuit.

- Assume for the purpose of illustration,

that. the subscriber A desires to communicate iclcgraphically with the subscriber B. The

subscriber A; wouldthereupon actuate switch 6, which establishes an. energizing circuit for relays 7 and 8 Obviously, however, this switch 6 1nay be.used..for other purposes, such as the closure of the power circuit extciuling-to the motor of the'printing telegraph equipment. For the sake of clearness,

the latteiahas not'been shown. Relay 7- in opening'its contact disconnects call bell printing telegraph 23, 1922. Serial No. 608,727.

-3 from the telegraph line D and connects the upper winding thereof to this line. Relay 8, injattracting its ,armature, opens at its contact a short circuit about resistance 9 which is now included in the locking circuit. of the relay 7, the transmitter and printer, the latter two having been shown diagrammatically. A printer of a type' suitable for use in connection with the system now under consideration is disclosed in U. S. Patent to H; Pfannenstiehl No. 1,583,865 granted May 4, 1926. It is understood, of course, that other types of printing telegraph equipment may be used with equally good results.

The closure of the .tront contact of relay 7completes an operating'circuit for line lamp extending from battery, through the lamp 15, tip contact'of the jack 4, armature and front contact and upper winding of relay 7 resistance 9, contact of break key .10, and the printing telegraph equipment to ground. -Line lamp 15 is thereupon lighted for indicating to the operator that subscriber A desires to be connected with another subscriber.

'lhe operator at the central ofiice in'observing the lighted condition of lamp 15, inserts plug 16 into'jack 4:, whereupon the circuit including the lamp-15 is severed, due to the movement of the tip contact of the jack 4. Theinsertion of the plug 16' into the jack 4 also establishes an energizing circuit for sleeve relay 17 extending from grounded battery, through the winding of relay 17 and the sleeve contacts of plug 16- and jack 4 to ground. Relay 1? in closing contact 18 establishes an energizing circuit for the right and left hand windings of re peater relays 20 and 21, respectively. This circuit may be traced from grounded battery, through the left hand winding of repeater relay 21, right hand winding of re peater relay 20 and contact 18 to ground. The establishment of the circuit just traced causes the operation of the armatures of the respective r'epeafer relays for closing their associated contacts. 'Each of the repeater relays closes'at one of its contacts the operating circuit of the other repeater relay, ihatis, repeater relay 20 in closing contact establishes. an operating circuit for re peater relay 21, extending from battery through the upper armature and back contact of relay 32, normal contact of printer 16 and jack 4, out 'over the line D to the subscribers station A and thence through the locking winding of relay 7, resistance 9,

break key 10 and the printer set to ground.

Contacts '25 and 27 of repeater relays 20 and 21, respectively, being now closed, these relays will remain operated. Follow- .ing the closure o'ficontacts 25 and 27, the

repeater relays 20 and 21 cause the closure of contacts- 2.6 and 28. ,Contact 19 of sleeve relay 17 being now closed, a short circuit for the righthand and left hand windings respectively of repeater relays 20 and 21 is established. This latter circuit may be traced from grounded battery, through the right hand back contact of supervisory relay 22, contact 26 of repeater relay '20, contact 28 of repeater relay 21, contact 19 of sleeve relay 17 and the back contact of supervisory relay 43 to ground. Accordingly no current flows through the right and left hand windings of repeater relays 20 and 21,

g respectively.

It is to be noted that for the condition just described current flows through the winding of supervisory relay 22, which current is not ofsui'licient strength to energize the same for the lighting of supervisory lamp 23. The operation of supervisory relay 22 will be described more fully hereinafter.

The plug 16 having been inserted in the jack 4,the operator is now in connection with the subscriber A. The operator thereupon actuates a printer key 31, which connects the printing telegraph equipment, which is common to a plurality of cord-circuits and which may beassociated with the other cord circuits upon the operation of printer key 33 or other keys a sociated with other cord circuits serially with the tip conductor of the link circuit. The operator may now actuate the transmitting mechanism for communicating with subscriber A to ascertain the number of the called for line. The subscriber Anow operates his transmitter to send a series of impulses for causing the-operation of the printer equipment at the central office for indicating to the operator the number of the line desired. For the case chosen for illustration the subscriber A would transmit a character or number designating the line E which extends from the central otfice to the subscribers station B.

- The operator having-ascertained the number', of the called for line inserts the calling plug 35 in the jack 5 for extending the line 'D to the line E. The insertion of the plug 35 in the jack 5 causes the disconnection of the line lamp 36 which is prevented from lighting when thesubscriber B responds to the call. Al o the insertion of the plug 35 into the jack ,5 causes the operation of sleeve relay 32 over a circuit extending from battery through the winding of sleeve relay 32 and the-sleeve contacts of plug 35 and jack 5 to ground. Sleeve relay 32 in operating opens at its contacts the operating cir suit of therepeater relay- 21, which is re leased and remains deenergizeduntil the subscriber B responds by the connection of the printer set thereat with the line E, as will be described hereinafter. Repeater relay 21 opens at its contact 27, the energizing circuit for the operatingwinding of repeater relay 20, but owing to the establishment'of the locking circuit for repeater relay 20, this relay does not open its contacts, but remains energized until the transmitter at station A is operated, at which time it responds to the impulses thus transmitted for repeating such impulses to the connected line after the connection has been estab-' lished.

The plug 35 being inserted in the jack 5, the supervisory relay 43 is connected with the ring conductor of the associated line. The supervisory relay 43 will, however, not be energized for causing the'lighting of supervisory lamp 44, on account of the call bell 38 and a condenser being connected serially with the tip conductor of the line E. It the operator desires to supervisethe connection the printer set associated with the link circuit should remain connected in the link circuit until the called for station responds; The operator inay now actuate ringing key 37 for impressing on the line E ringing current. The ringing .current impressed on the line E traverses the armature and back contact of relay 40 the call bell 38 and' associated condenser to ground,

the call bell 38 thus responds for indicating the upper winding of relay 40 and through resistance 42. break key 46 and the printer set, associated; therewith to ground. The

short circuit about the resistance 42 having been removed upon the operation of relay 41, the printing telegraph equi'pment in station B is'now operatively associated with the line E extending to the central station C. The establishment of the circuit just traced also completes an energizing circuitfor the repeater relay 21 extending from grounded battery through the ring contacts of jack and plug 35, winding of super-. visory relay 43, lower front contact and armature of sleeve relay 32, auxiliary con: tact of repeater relay 20, right hand winding of repeater relay 21, right hand contact of release key 30, through operatorsprinting telegraph set,upper armature and front, contact of-sl eeve relay 32, contact of ringing key 37, tip contacts of plug 35 and jack 5 and thence over the line- E, through the upper winding of relay 10, resistance 42, break key 46 and the printer set to ground. I

The subscriber B now operates his transmitter for transmitting to the station A through the link circuit C, a series of impulses, which upon being received on the printer setvat station A informs such subscriberthat B is now ready to receive the communication from the former station. The printer key 31 at the central siation being actuated, the impulses transmitted from station B to station A will accordingly' be received on the printer equipment thereat, indicating to the operator that the called-for subscriber has answered at which time the printer ikey thereat may be restored to normal. l

Following the completion of the communication between stations A and B, the subscriber at station B opens key 39, whereupon the circuit extending from grounded battery, through the lower winding ofrelay 40 and the winding of relay 41, is broken. Re.- lay 40, however, does not release its arma ture, owing to current flowing through ils upper winding. Relay 41, however, does release its armature for short-circuiting resistance 42. The short circuiting of resistance 42 causes a change in the current flowing through the supervisory relay 43 which is such that thisrelay operates.

Belay 43 in operating, closes at its front contact, an operating circuit for supervisory lamp it-4t which is'thereupon lighted for indicating to the operator that the plug 35 may be disconnected from the jack 5. Similarly, when the subscriber at station A opens switch 6, the resistance 9 being now short circuited, supervisory relay 22 is accordingly energized for lighting the supervisory lamp 23, the purpose of which is the same asthat described in connection with supervi- -sory lamp a l. Supervisory relay 43, in openconnection has been broken down.

so? B about the right hand winding of repeater relay 20, whereupon this relay is maintained energized over a circuit extending from grounded battery, right hand armature and contact' of relay 22, contact 26 and right hand winding of repeater relay 20 toground at either the uppermost contact and arma-' ture of relay 17 or the middle contact and armature of relay 32; Now should the subscribcr A operate his transmitting mechanism, impulses will not be repeated to line 1 E as repeater relay 20 is now held energized over the circuit justtraced.

Likewise when supervisory relay 22 is energized theshort circuit about the let"; hand winding of repeater relay 21 is removed, ac cordingly preventing it from responding to the actuating of the transmitting equipment at station B. Such a condition also insures that the supervisory clamps-23 and 44 will be maintained lighted until the operation of release key or the removal of the plugs 16 andfrom their associated jacks. If the locking circuit for the repeater relays wasonot esiablishednpon the operation of thesuperviso'ry relays, thenupon the operation of switches 6 and 39 atvthe respective stations for associating the printing telegraph equipment with the line, the supervisory relays would be deenergized; and the lamps controlled thereby extinguished. Accordingly the operator would not receive the disconnect signal unless it happened to be observed upon its initial operation, that is, immediately following the opening of the switches 6' and 39 at stations, A and-B, respectively. Before disconnecting the plugs from the associated jacks, release key 30- should be operated momentarily by the operator to open the circuit of both answering and calling plugs, thus releasing relays 7 and 40 and restoring the subscriberscircuits to normal. V

Assume, for example, that the subscriber A desires to recall the operator before the Subscriber A' thereupon operates repeatedly flashing key for shortcircuiting the resistance 9. Resistance 9, beingshort circuited, the current now flowing through the winding of supervisory relay 22.is such that this relay is operated for causing the'illumination of the supervisory lamp 23. The operator C, observing the flashing of the supervisory lamp 23 is informed that 't he subscriber A desires to be connected withanother subscriber? Accordingly the operator actuates printer key 31 for connecting the printer set thereat with the cord circuit. The operation of the system from this point vis identical to that previously described.

During the period that any of the subscribers is reeiving impulses from any other subscriber, such subscriber may interrapt the transmission byact-uating a break key located at each of the subscribers? stations. B desire to interrupt the sending; of the subscriber A, it would only be necessary to actuate break key 46, thereby opening the en'- ergizing circuit for repeater relay 21 for producing a condition which informs the subscriber A that subscriberB desires to reversethe direction of the sending.

Referring now to Fig. 2 there are shown trunk circuits 60 and 61 which extend from I distant stations and terminate at a central office F in jacks 62 and 63 respectively. Each of the trunk circuits as associated there-" with duplex equipmei. or permitting half duplex service between the connected stations. The equipment for one line only has" been shown in detail as'the equipment for the other line is identical to that shown in the upper left hand corner of Fig. 2. In

will be free from bias and distortion. There is also arranged with 'such repeating means switching relays for pertorming desired functions as will be described more fully hereinafter.

The repeating or regenerating equipment- G which is associated with the link circuit comprises a distributor including a plu-' rality of rings 72, 73, 7 i and and a brush arm 76, the latter being frictionally mounted on a continuously rotating shaft 77. The brush arm 7 6 is released upon the energiza tion of a release magnet 78, under the con-' trol of the brush carried by the brush arm 76, the start control relay 71 andthe line relay 79. The segments of the ring 74L are 7 in number, one corresponding to each unit of the five-unit code for which the system is v established, the sixth serving as a stop segment, while the seventh serving'to etlectthe transmission of a starting impulse to the distant or receiving station upon the passage of the brush carried by the arm 76" thereover. Alternating ones of the segments forming the ring 74 are connected with the armature of polarized storing relay 81 which serves for storing the impulses sequentially to be transmitted while the remaining ones thereof are connected with the armature of a similar storing relay 82 serving thesanie purpose as storing relay 81. These relays S1 and '82 are ofithe polarized type and thereby when either is energized their armatures- The outer ring 7 2 comprises a plurality of segments the length of which'are approximately the length of the segments form- For example, should the subscriber.

Equipment similar to that designated by the numeral 7 0 is shown at-85 for regenerating-and repeating signals to be transmitted the opposite direction. Inasmuch as such equipment is identical to that just described, a detailed description thereof is considered unnecessary here. r

Theop'eration of the system is as follows Assume that a party to-Whose stationithe trunk circuit 60 extends desires tocommunicate telegraphically with a party -whose printing telegraph equipment is operatively associated Withthe trunk circuit 61. The calling party will thereupon operate his transmitting equipment or may for the purpose of signaling the operator me're-lyopen. the linecircuit for causing the energization of the-line relay at the central .oflice F to reverse the position of its armature. Line relay.99responding'to the alteration of-the normal line condition causes the deenergization of control relay- 91. This control relay atits left hand contact opens the ci'rcuit of the pole changer relay 92 while at its right hand contact a short circuit about the lower winding of the pole changer relay 92 is removed. Accordingly; pole changer relay 92 will not reverse'the position of its armature due to the establishment of an energizing circuit through the lower winding thereof. The control relay 91 upon being deenergized also opens the operating circuit of line relay 93 which becomes deenergized causing the lighting. of line lamp 94. Relay 93 -closes at its left hand contact a short circuit about its left hand winding wherebv lamp 94 is maintained lighted.

The operator atthe central ofiice observ-v ing the lighted condition of the line lamp 94 inserts plug 95 into jack 62. The insertion ofplug 95 into jack 62 opens at the tip contact of the latter the operating circuitv of line relay 93 whereby the original energizing circuit of this relay is severedl However, a circuit is established for operating this relay extending from grounded battery through the winding of sleeve relay .96,

sleeve contacts of plug 95 andjack 62 and.

ion

the right hand winding of line relay 93 to ground. Both sleeve relay 96 and line relay 93 are thereby energized. Line relay 93..

opens the operating circuitof-the line lamp 94 which is thereupon extinguished. Sleeve relay 96 on the other hand closes at its upper contact. an operating circuit including the winding ofcontrolrelay 97 and the locking windings of line relays 79 and 98. The cir- .cuit for operating the relays just described may be traced froingrounded batterythrough the left hand 'winding's. of line re' lay 98- right hand winding of line relay "79,

winding of control relay 97, and the upper contact and armature of sleeve relay 9.6 to

ground. Control relay 97 in closing its right and. contact closes the power circuit extending to themotor which drives the shafts upon which the distributor brush'arms are mounted. Line relays 79 and 98 in energizing connect negative battery with the continuous rings 73 and 73' respectively. Due to the fact that negative battery is now connected withthe continuous rings in each case, and since the brush arms 76 and 76' are atrest; an operating circuit is established for release magnets 78'and 78'. The energizing circuit for the release magnet 78 may betracedfrom negative battery at the contact of line relayi79, continuous ring 73, outer brush carried-by the brush arm 76, segment 80,- winding of release magnet 78, armature and lower contact of start control relay 71 to the positive terminal of the battery. Likewise, the energizing circuit of the release magnet 7 8T.may be traced from the negative fiole of battery .by thecontact of the line relay 98, continuous ring 73-, outer brush carriedby the brush arm 76', segmentSO', winding of release magnet 7 8' and the armature and lower contact of start control relay 71 to the positive pole of the battery. Both of-the release magnets 78 and 78 are accordingly energized for removing the latches controlled therebyout of the path of the respective brush arms. As previouslyldescribecl, the bIUSh'i'HIHIS 76 and 76' are frictionally mounted on continuously rotating shafts. When the release latches are withdrawn the brush armsthereupon are'free to rotate. v

As the brush arms rotate the brushes carried thereby travel over the receiving segments whereby negative impulses 'will be transmitted through the storing relays 81 and 82 and relay 7 1. The armatures of-relays 81 and 82,wil lthus be moved to engage their lower. contacts thus connecting ground with the transmitting segments while the armature of relay 71 engages its uppercontact. When'the sending brush of eachdistributor reaches segment #1 the sending relays 100 and 101 will be operated and will re: main operated until the brush completes its cycle of rotation. Following the passage of the brush arm'over segment#5 the brush arms in each case will be arrested and will be held against rotation until the receipt of a start impulse froineither of the stations to which the circuits and 61 extend. Release magnets 78 and 78 will not be energized upon the engagement cf the outer brush d 80 negative furnished from the trunk circuit over the ring contacts of jack 62 and plug 95, upper contacts of relay 190 and the left hand winding of line relay 79 out over the tip contacts of plug 95 and jack 62 to the'terminal of the battery. The current for line relay 98 is, however, furnished from battery .on the lower armature and contact of sleeve relay l08,the circuit of which extendsthrougli the right hand windings of line relay 98, upper .contact and armature of'sending relay 101, .right hand contact of printing key 102, middle armature and contact of sleeve relay 108 to ground. Accordingly, these line relays will remain energized even though short circuits are placed about the holding windings thereof. The operator may now. actuate printer key 102 which disconnects the conductors 103. extending to the other cord circuits where a key similar to key 102is located andalso connects the-printer set located thereat in series with the operating circuit of line relay 98. As sending. relay 101 is now energized any signals transmitted by the operator will be repeatedby line relay 981through the distributor 85 to the storing relays 81 and 82. Similar signals will then be retransmitted by the sendin'g'br'ush and repeated by sending relay 100'over the trunk. circuit to, which the plug is connected. The signals transmitted by the sending relay will pass through the operating winding-s of line relay'79 but the latter relay will not be afl'ected as'itis held operated by its holding winding during the intervals when the circuit in its main winding is open.

The party initiating the call will after receiving the response ofthe operator operate the transmitting equipment for the transmission of a series of character signals for informing the operator the number of the trunk circuit towhich connection is desired. In this case the line relay-79 responds upon the receipt of a starting impulse to cause the application of a positive-battery to the continuous ring 73 and accordingly the energization of the release magnet 7 8 and the release of the brush arm 76. As the brush arm 76 travels over thereceiving segments and since receiving relay 79 responds to the operation of the receiving relay 90, in ac. cordance with the transmitted signals, impulses will be stored in the storing relays and 852. Thus,

s nd] ng d for o upon the passage ot the 'ductors of the cord circuit.

trunk circuit 61, inserts plug 105 into jack 63. The insertion of the plug 105 into jack 63 causes the opening of the main operating circuit of line relay 106. This line relay however is not deenergized as the insertion of the plug 105into jack 63 establishes an energizing circuit for sleeve relay 108 and the left hand winding of line relay 106. Accordingly, line lamp 107 is not "lighted.

Sleeverelay 108 also connects the operating winding of the line relay 98 and the repeating equipment with the tip and ring con- The system is now in a condition for normal operation.

The operator may now actuate his transmitter for transmitting to the calling and called for subscribers characteristic characters for informing such parties that connection has been established and the transmission of messages may he proceeded with. In case the plug 105is inserted inthe jack 63 when the plug is pulled down, sleeve relay108 will be operated and sleeve relay 96 accordingly released. In this case the locking circuit for the line relays 79 and 98 will be completed through the control relay winding and the upper front contact of sleeve relay 108 and the circuit for the auxiliary contacts of sending relay 100 will be open at the lower armature and contact of sleeve relay 96. Under this condition line relay 79 will be held operated by its lockingwinding although there is no current in its operating Winding. If the printing key 102 is now operated the operators printer set will be connected directly in series with the plug 105 for communication over the con; nected trunk circuit.

The transmission of impulses in either direction causes the operation of the line relays for releasing the associated-distributor, storing the impulses in accordance with those transmitted and retransmitting such impulses to the connected trunk circuit which will be free from bias and distortion.

In order that either party may inform through auxiliary contacts on line relay 79 and by slow charging condenser112;v This condenser 112 is connected to a high resistance 113 which limits the current to such a value that condenser 112 requires several seconds to become charged to approximately full potential of-the battery. When line relay 79 is operated supervisory relay which is of comparatively low resistance is shunted around the condenser 112 which preventsthe condenser from receiving, any appreciable charge. Resistance 113 also limits the current to a value such that supervisory relay 110 will not be energized except when line relay 7 9 is deenergized to open the auxiliary contacts associated therewith for an appreciable period of time, that is,

for a time longer than the time occupied in the normal transmission of impulses. Thus, if the party at the station of the trunk circuit (SO-desires to advise the operator of the completion of the communication with the connected trunk circuit, it only becomes necessary to cause the transmission of a long open impulse. This open impulse upon being-received at the central oilice causes the opening of the auxiliary contacts of line relay 79 allows condenser .112 to charge slowly to approximately the full potential.

of the battery. At the end of the long open mpulse, line" relay 79 Wlll operate to close its auxiliary contact, thus allowing condenser 112 to discharge through thewindreleased upon the actuation of key 102- and the withdrawal of the plugs 95 and 105.

It is apparentfroin the previous description that the pre'sentinvention provides an arrangement whereby a number of trunk circuits extending from various subscribers stations to a central ofiicemay be established between the var'ious'lines by means of .cord circuits, such cord circuits being equipped with repeating means for repeating the 1m ulses from one line to another which are ree from bias and distortion.

Although the invention has been disclosed and described in conjunction with a particular type of system'it is, of course, obvious that various departures may be madewithout departing from the spirit and scope of the present invention.

What is claimed is:

1. A printing telegraph system comprising a plurality of printing telegraph subscribers lines terminating at a central ofi' ice, link circuits at the central office for connecting any of'thesubscribers lines 'with 'any other 'subscribers line, relay means in each link circuit operative in accordance With the transmitted impulses for repeating impulses between connected lines, and other means in each link circuit cooperating with said relay 1 means for reforming received impulses to Ill insure the repetition thereof in the same form as originally transmitted.

2. A printing telegraph system comprising a plurality of printing telegraph subscribers lines termina'ting at a central office,

a plurality of link circuits at the central oflice for establishing connections between any of the subscribers lines, relay means in each link circuit for repeating impulses be tween connected lines, and-means in each link circuit cooperating with said why means for reforming the received impulses to insure their repetition in their original form between connected lines.

3. In a printing telegraph exchange system, a plurality of printing telegraph subscribers lines terminating at a central office, link circuits at the central ofiice for connecting any of the subscribers lines with any other subscribers line, and means in each link circuit comprising distributing apparatus, a plurality of relays associatedwith said distributing apparatus and arranged to be selectively operated, and circuit connections established by said distributing apparatus for repeating to a connected line impulses in accordance with the operation of said relays.

4. In a printing telegraph exchange system, a plurality of printing telegraph subscribers lines terminating at a central oflice, interchangeable link circuits at the central ofiice for establishing connections between any of the subscribers lines, means in each link circuit comprising an intermittently rotating distributor, a pair of relays associated therewith to be selectively operated in accordance with the impulses transmitted, a source of signaling current, and circuit connections established by said distributor tween any of the subscribers lines, means in each link circuit comprising a start-stop distributor having receiving and transmitting sections, storing means selectively operated by current impulses received from one at the connected lines, a source of signaling current adapted to cooperate with the transmitting section of said distributor, means to retransmit to the other connected line from said current source corresponding impulses, the cooperation being controlled by said storing means whereby signaling current impulses will be originated.

6. A printing-telegraph exchange system comprising aplurality of printing telegraph subscribers lines terminating at acentral olfice, a plurality of operators cord circuits at the centralbfiice for establishing connections between any two of the subscribers lines, means in said cord circuits for repeating impulses between connected lines, said last-mentioned means comprising means for insuring thatthe impulses as repeated are of the same form as those transmitted, and

means in each of said cord circuits for enabling an operator to supervise a connection after it has once been established. a

In testimony whereof, I have signed'my name to this specification this 22nd day of December, 1922. I

GILBERT s. vERNAM. 

